you should be going to your doctor for a blood test, because you can be pregnant. some women can be pregnant and not knowing because they only took a hpt. a hpt calculates the hcg level in your urine to determine your pregnancy or not, so not many can identify with this type of test, so try and go to the doctor, and explain to him what is happening, and that you think you might be pregnant, they will give you a blood test so then you will know forsure.
I dont think your pregnant, esp AFTER 8 days. Prolly an off cycle. If your period doenst come in another week id get checked.
It sounds like you could be pregnant and just tested too early sometimes the pregnancy hormone doesnt appear as early as the over the counter test kits require meaning you should retest and then follow up with your doctor and if your not pregnant after that a more serious issue could be involved. Good Luck with whatever happens